Voltage regulator device



FIG.2

M. SAPOFF ETAL VOLTAGE REGULATOR DEVICE Filed April 12, 1962 June 29, 1965 wk S INVENTORS ilk-YE? SAPOIF BY faaaer/Mdp zwwemz WW ArraeA/Q Cueezwr Sap/ 4 Y FIG. 4

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Av ur United States Patent 3,192,469 VOLTAGE REGULATOR DEVICE Meyer Sapoff, West Orange, and Robert M. Oppenheim,

Colonia, NJ., assignors to Victory Engineering Corporation, Springfield, N.J., a corporation of Delaware Filed Apr. 12, 1962, Ser. No. 186,927 6 Claims. (Cl. 323-68) This invention relates to a voltage regulator for maintaining a constant voltage across a pair of output terminals while a pair of voltagesupply terminals connected to a source of supply may vary over a wide range of voltage values. The invention has particular reference to a voltage regulator which does not use amplifier equipment such as a series of vacuum tubes or transistors and relies entirely upon the impedance characteristic of a thermistor. 7

'Many voltage regulator circuits have been designed and used for the maintenance of a constant voltage across a pair of output load terminals. Some of these systems use comparatively simple circuits but provide a large range of output voltage variation which is not satisfactory for accurate work. Other voltage regulators do maintain an output voltage within a very narrow restricted range, but in order to do this they must employ a number of amplifier stages together with additional power supplies and other complicated circuit equipment. The present invention can be relied upon to maintain the output voltage within a range of .01% without any amplifier stages and using only a thermistor and an ordinary resistor. The only requirement being to maintain the thermistor at a constant temperature.

An object of the present invention is to'provide an improved voltage regulator which avoids one or more of the disadvantages and limitations of prior art arrangements. l

Another object of the present invention is to provide a voltage regulator which performs equallywell with a direct current supply or with an alternating current source of power.

Another object of the present invention is to provide a standard alternating current source of potential which can be used in the laboratory for testing other circuits and for calibrating instruments.

Another object of the present invention is to reduce the cost and weight of voltage regulator systems.

Another object of the present invention is to increase the life of voltage regulators by employing circuit components which last almost indefinitely.

A further object of the present invention is to reduce the space occupied by voltage regulator systems.

The invention comprises a pair of input terminals for the application of electrical power from a power supply circuit. A pair of output terminals are arranged for connection to a load which is to be maintained at a constant voltage. The regulator circuit includes a resistor and a thermistor connected in series and bridged across the output terminals. The thermistor and resistor form an integral assembly in which the resistor is mounted adjacent to the thermistor and is non-inductively wound to a value which is equal in magnitude to the slope of a linear portion of the negative resistance portion of the voltage-current characteristic of the thermistor. This integral matched thermi-stor resistor network is mounted Within a heat-sink which is characterized by a large heat capacity and thereby integrates temperature fluctuations of the thermistor-resistor sub-assembly to minimize the effects of such fluctuations. The ambient temperature of the thermistor resistor network is maintained constant by an electrical heater which is mounted adjacent to the heat sink and which receives electrical power from a controlled source of supply. The input 3,192,469 Patented June 29, 1965 terminals and the output terminals are connected respectively to each other with one of the connections including a series impedance.

For a better understanding of the present invention, together with other and further objects there-of, reference is made to the following description taken in connection with the accompanying drawings, and in which:

FIGURE 1 is a cross-sectional view of a thermistorresistor network and heater unit together with a cylindrical heat sink according to the present invention.

FIGURE 2 is a cross-sectional viewof a supporting means for holding the unit shown in FIGURE 1. This view shows a container supporting a vacuum jacketed flask in which the thermistor resistor network is supported.

FIGURE 3 is a graph indicating how the thermistor characteristic can be combined with a resistor to produce a fiat top curve having a range within which the voltage does not change with a change of current.

FIGURE 4 is a schematic diagram of connections showing how the voltage regulator circuit is connected between a supply and a load.

Referring to FIGURE 1, a thermistor 10 is supported on two lead-in conductors 11, 12, which are sealed in the wall of a glass container 13 which maybe evacuated or contain a gas. The thermistor 10 may be any one of a number of known ceramic mixtures which change their resistance characteristics as the current through them is changed. The envelope 13 is generally surrounded by a sleeve of dielectric material 14 upon which a resistance wire 37 is wound. The resistor 37 is connected in series with the thermistor to form a thermistor-resistor net work. The coil of resistance wire 37 is generally protected by a second cylinder 16 of thin insulating material such as mica. A cylindrical sleeve of copper 19 or other suitable heat retaining material is slipped over the insulating material 16, and hereinafter referred to as a heat sink. A resistance heating wire 15 is wound about the heat sink 19. The resistance heater '15 is connected to a controlled current supply 38. When the heat sink 19'is warmed, fluctuations in temperature in the heating wire will be evened out so as to maintain a constant tempera ture about the thermistor.

The thermistor 10 does not have a constant resistance and its current-voltage characteristics are shown in FIG- URE 3, curve 17. From this curve it is obvious that the resistance is a constant value from a small portion of its current carrying characteristic. When more current is applied, the voltage then drops and exhibits what is known as a dynamic negative resistance. It still more current is forced through the thermistor the voltage then increases.

The slope of the negative portion of the curve represents the value of the negative resistance of the thermistor. if such a thermistor is connected in series with an ordinary resistor having a positive resistance as represented by line '18 with a slope equal but opposite to the negative resistance portion of curve 17, there will result an overall volt-current characteristic 20 which has a horizontal portion A. It is obvious from this graph that as long as the current values are maintained between points 21 and 22, the voltage across the combination will remain constant.

The assembly of thermistor 10 and resistor 37, heater 15 and heat sink 16 as indicated in FIGURE 1 is housed within a container 23 (FIGURE 2) in order to further maintain its temperature at a constant value. The combination is mounted between a series of felt pads 24 at one end and a similar pad 25 at the other end with a cavity for bringing out the lead-in conductors and other control wires 27. The above described combination is mounted within a vacuum jacketed vessel 26, generally called a Dewar flask. This vessel is packed in a quantity of shredded heat insulation such as loosely packed felt or spun glass. The felt pad may be arranged to fit into an insulator base 28 which supports a plurality of contact metal pins 27 for engagement by a socket (not shown) whose terminals are connected to other parts of the regulator circuit. It will be obvious that many changes may be made in the structure shown in FIGURE 2, and other types of heat insulation structures may be employed to keep the heat conductivity at a minimum value.

The entire voltage regulator circuit is shown in FIG- URE 4 where a pair of input terminals 30, 31, are for connection to a power supply which may be either alternating or direct current. A pair of output terminals 32, 33, are also provided for connection to a load 34. One of the input terminals such as 31 is connected directly to one of the output terminals 33 by a conductor 35. The other terminals and 32 are connected by a conductor having a variable resistor 36 in series therewith. The combination of thermistor 10 and resistor 37 are series connected across the output terminals 32, 33. The heater resistor 15 is connected to a controlled current supply 38 which may be a storage battery connected in series with an adjustable resistor. For more accurate temperature control, a thermocouple 40 is positioned within container 23 in close proximity to the thermistor envelope. The thermocouple is connected to a control means associated with the current supply 38 so as to maintain a constant temperature in container 23. The control means may be a relay or a transistor, these components and their applications being well known in the art.

The operation of this circuit is as follows: When the input voltage changes or when the load value changes, an increase or decrease of current flowing over conductor 41 results. This change will produce a change of current through resistor 37 and thermistor 10 but the voltage across the combination and across the output terminals will remain the same. Any change of voltage across the input terminals will appear across resistor 36. If the variation of voltage across the input terminals is permanently increased to some higher value, the resistor 36 can be adjusted to take care or" the increase and reduce the current value through the thermistor to a value which lies within the range A as indicated in FIGURE 3.

From the foregoing it will be evident that a simple and eflicient voltage regulator has been described and illustrated which can be employed to maintain a pair of out put terminals at a desired voltage. The regulator can be made to operate on either alternating or direct current and its operation is not influenced by a change of frequency.

Having thus fully described the invention, what is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A voltage regulator device comprising, a pair of input terminals for the application of an electrical power supply, a pair of output terminals for connection to a load, a constant voltage circuit connected across the output terminals for maintaining the output voltage constant, said circuit including a resistor and a thermistor in series,

said thermistor having a volt-ampere characteristic which includes a negative resistance portion, a sealed envelope containing said thermistor and a gas, an electrical heater mounted on the outside of the envelope and the resistor for maintaining a constant temperature of the gas in the envelope, a source of electrical power connected to said heater; and connections from the input terminals to the output terminals, one of said connections including a series impedance.

2. A voltage regulator device comprising, a pair of input terminals for the application of an electrical power supply, a pair of output terminals for connection to.a

load, a constant voltage circuit connected across saidoutput terminals for maintaining the output voltage constant, said circuit including a resistor and a thermistor in series, said thermistor having a dynamic negative resistance for a restricted portion of its operating characteristic, said resistor having a resistance value equal to said negative resistance for producing a combination having a constant voltage over said restricted portion, a sealed envelope containing said thermistor and a gas, an electrical heater mounted on the outside of said envelope for maintaining a constant temperature of the gas in the envelope, a source of electrical power connected to said heater, and connections from the input terminals to the output terminals, one of said connections including a series impedance.

3. A voltage regulator device as claimed in claim 2 wherein said series impedance is adjustable for matching variable ranges of input voltages.

4. A voltage regulator device as claimed in claim 2 wherein a temperature-sensing means is mounted within said envelope and is connected to a control circuit which maintains the gas in the envelope at a constant predeten mined temperature.

5. A voltage regulator device as claimed in claim 2 wherein said envelope is positioned within a double-walled container.

6. A voltage regulator device as claimed in claim 2 wherein said electrical heater is wound on a heat sink metal cylinder.

References Cited by the Examiner UNITED STATES PATENTS 2,533,287 12/50 Schmitt 323-68 2,743,413 4/56 Johnson 32369 2,824,278 2/58 Johnston 323-69 2,949,575 8/60 Shadle 323--68 3,040,158 6/62 Cutler et al. 219-210 3,122,199 2/64 Bylotl 323--69 3,122,316 2/64 Leigh et a1 317--132 OTHER REFERENCES Electronic Engineering, Thermistors by W. Rosenberg, pages 187, June 1947.

Technique of Microwave Measurements, by C. G. Mountgomery, pages 89-97, 1947, 1st edition.

LLOYD MCCOLLUM, Primary Examiner. 

1. A VOLTAGE REGULATOR DEVICE COMPRISING, A PAIR OF INPUT TERMINALS FOR THE APPLICATION OF AN ELECTRICAL POWER SUPPLY, A PAIR OF OUTPUT TERMINALS FOR CONNECTION TO A LOAD, A CONSTANT VOLTAGE CIRCUIT CONNECTED ACROSS THE OUTPUT TERMINALS FOR MAINTAINING THE OUTPUT VOLTAGE CONSTANT, SAID CIRCUIT INCLUDING A RESISTOR AND A THERMISTOR IN SERIES, SAID THERMISTOR HAVING A VOLT-AMPERE CHARACTERISTIC WHICH INCLUDES A NEGATIVE RESISTANCE PORTION, A SEALED ENVELOPE CONTAINING SAID THERMISTOR AND A GAS, AN ELECTRIC HEATER 